Controlled suspension polymerization process without mechanical agitation

ABSTRACT

Non-Newtonian fluids, such as partially polymerized monomers or solutions of polymer in monomer may be pressure atomized below the free surface of a continuous liquid phase to produce a dispersed phase. A uniform or customized droplet size distribution can be obtained by imposing a required pressure pulsation on a flowing monomer upstream the atomizer inlet. This initial particle size distribution can be maintained or modified during subsequent polymerization process in a low shear, controlled turbulence flow pattern, created without mechanical agitation within the continuous liquid, by continuously or periodically injecting an inert gas at selected locations within the reactor.

FIELD OF THE INVENTION

The present invention relates to the concurrent or sequentialapplication of atomization technology to pressure atomizing aNon-Newtonian liquid in order to form a dispersed phase having acontrolled particle size distribution within another liquid, typicallyimmiscible, which forms a continuous phase and to maintain or modifythis initial particle size during the subsequent polymerization processin the continuous phase contained in a vessel, using a method to createwithout mechanical agitation a low shear, controlled (preferably low)turbulence flow pattern within a continuous liquid, by continuously orperiodically injecting and preferably recycling a neutral immisciblelighter (less dense) fluid, preferably gas, below the free surface ofthe continuous phase. In one preferred embodiment the liquid beingatomized is a partially polymerized mixture of one or more monomers andis subjected to pressure pulsation upstream the atomizer inlet. In otherembodiments of the invention the gas is injected into the reactor tocreate bubbles either substantially larger or at least an order ofmagnitude smaller than the average size of the dispersed phase.

BACKGROUND OF THE INVENTION

The present invention teaches the application of high pressureatomization as the method to disperse an organic phase. It has beenproposed to atomize and coat monomer droplets in an aqueous medium toform a suspension (Review article E Vivaldo-Lilma et al., An updatedreview on suspension polymerization. Ind. Eng. Chem., (36) (1997) of S.Matsumoto et al., A production process for uniform-size polymerparticles. J of Chem. Eng. Of Japan, vol. 22, No. 6 1989), using coaxialnozzles and injecting the monomer mixture through the inner nozzle andthe coating composition through the outer nozzle. The shell of theresulting coated particle is hardened chemically or physically to form acapsule which may be suspended in water and polymerized. Subsequent topolymerization the outer shell is removed from the polymer. The presentinvention has eliminated an essential feature of the art, as it does notcontemplate the formation of a shell about the monomers.

Comparable encapsulation technology is disclosed in U.S. Pat. No.4,427,794 issued Jan. 24, 1984 assigned to Bayer A. G. Rather than usingcoaxial nozzles, the patent teaches an encapsulation medium separatefrom the continuous aqueous phase. As noted above the present inventionhas eliminated the essential feature of encapsulation required by thisreference.

U.S. Pat. No. 5,061,741 issued Oct. 29, 1991, assigned to MitsubishiKasei Corporation discloses a method for preparing oil in water typedispersions. The oil is a monomer or monomer mixture which is notpre-polymerized (i.e. a Newtonian liquid to be atomized). The referencefails to teach or suggest the atomization of a non-Newtonian liquid asrequired by the present invention. Further the reference fails to teachthe application of elevated pressure to atomize the oil (monomer) phase.Additionally, the reference teaches the monomer and continuous phasesare at relatively low temperatures not exceeding about 30° C. A criticalfeature of the reference is the use of a disperser plate having nozzlesin an annular design. The patent teaches away from the present inventionin that a disperser plate having an annular layout for the nozzles isnot required and the atomizing nozzles may be uniformly distributed overthe disperser or orifice plate.

U.S. Pat. No. 3,922,255 issued Nov. 25, 1975 assigned to Rohm and HaasCompany teaches atomizing unpolymerized monomers into a continuous waterphase. The monomers are not polymerized and therefore are Newtonian.Further the reference fails to teach applying a pressure pulsation tomonomer feed to the atomizers. The reference fails to teach the subjectmatter of the present invention.

There is a series of patents in the name of Timm, assigned to the DowChemicals Company which teach dispersing monomer droplets in acontinuous phase by subjecting a jet of a monomer mixture to vibratoryexcitement. This art includes U.S. Pat. Nos. 4,444,961; 4,666,673; and4,623,706. The references fail to teach atomization of a non-Newtonianliquid. Further the references fail to teach the application of highpressure to the phase to be atomized. Further the flow rate of theatomized phase of the Timms references appear to be up to an order ofmagnitude lower during the dispersion process than the flow rate of thepresent invention.

The present invention further teaches to process polymerize thedispersed phase in a flow pattern in a continuous phase created by gasinjection. There is a prior art relating to the injection of gas into acontinuous liquid phase in sparging and, less often, surface aerationsystems. Mechanically agitated tanks are usually used for this task andthe main purpose of these systems is to disperse a gaseous componentwithin a liquid component, (e.g. ethylene gas in liquid styrene) forfurther processing. Other applications involve high pressure gasinjection to aid mechanical agitation/stirring by intensifying themixing and increasing turbulence level in a stirred tank. All thesesystems operate in highly turbulent regimes and are equipped withmechanical agitators, (Wessner et al, 2002, Nienow et al 1977, Nienow etal., 1985a, Tatterson 1991, Bujalski 1988, Warmoeskerken et al 1984,Chapman et al, 1983). These references teach the technology based on theprinciples which are quite opposed to the ones proposed in the presentinvention in that a low shear, low turbulence flow pattern is created inthe reactor by gas injection and no mechanical agitation is required.There are also numerous applications of in situ gas injection toremediate contaminated aquifers or soil matrix, but they serve a totallydifferent purpose and operate also on different principles than processdescribed in the present invention.

The present invention seeks to provide a process to pressure atomizenon-Newtonian immiscible liquids into a continuous liquid medium andmaintain, improve, or alter (reduce) the dispersed droplet size duringthe subsequent polymerization process by the controlled recirculation ofan inert gas through the continuous liquid medium.

SUMMARY OF THE INVENTION

The present invention provides a process comprising pressure atomizingfrom 0.01 to 60 volume % of a non-Newtonian immiscible liquid having adensity ±20% of the density of the continuous phase, at a pressure of atleast 5 bar, below the free surface of a continuous liquid phase whichmay be stationary or flowing, contained in a tank, pipe or loop vessel,to produce a dispersion of atomized droplets having at least onecontrolled average diameter from 0.1 mm to 10 mm and to maintain ormodify this initial size distribution during the subsequentpolymerization by distributing the dispersed phase in a controlled lowturbulence flow pattern, created without mechanical agitation in acontinuous phase by continuously or periodically injecting at gaugepressure up to 15 bar into selected parts of the reactor one or morestreams of gas inert to the reactor contents having a density lower thanthe continuous phase and immiscible with the reactor contents andrecovering this gas from the top of reactor, above free surface of thecontinuous phase. Preferably the gas is recycled back to the injectionports of the reactor.

In one preferred embodiment the liquid being atomized is a partiallypolymerized mixture of one or more monomers and is subjected toinstantaneous pressure pulsation Upstream the atomizer inlet.

In other embodiments of the invention the gas is injected into thereactor to create bubbles either substantially larger or at least anorder of magnitude smaller than the average size of the dispersed phase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall schematic diagram of the experimental setup used toatomize the partially polymerized monomer.

FIG. 2 is a schematic diagram of the vessel used to conduct thepolymerization experiments.

FIG. 3 is a sectional view at A—A of FIG. 2.

FIG. 4 is a comparison of the initial size distributions of pressureatomized droplets of partially polymerized to 35% styrene monomer andthe resulting beads, which were polymerized in a flow pattern of thepresent invention in accordance with example 1. The droplets and thepolymerized beads were taken as the random samples for the respectivepopulations.

FIG. 5 is a comparison of diameters of the pressure atomized droplets ofstyrene monomer partially polymerized to 35%, the droplets taken as arandom sample, and the resulting polymerized beads, which werepolymerized in a flow pattern of the present invention in accordancewith example 2, taken also as a random sample.

FIG. 6 shows the comparison of the size distributions (cumulative weightpercentage oversize) of the pressure atomized droplets of styrenemonomer and the resulting polystyrene beads polymerized in flow patternof the present invention in accordance with example 2, and whose sizeswere shown in FIG. 5.

FIG. 7 is a comparison of diameters of the droplets of styrene monomerpartially polymerized to 35%, pressure atomized at ambient temperature,with modulation frequency 80 Hz and amplitude less than 8% of staticpressure of the monomer, the droplets taken as a random sample, and theresulting beads, taken also as a random sample, which were polymerizedin a flow pattern of the present invention in accordance with example 3.

FIG. 8 shows the comparison of the size distributions (cumulative weightpercentage oversize) of the pressure atomized droplets of styrenemonomer and the resulting polystyrene beads polymerized in flow patterof the present invention in accordance with example 3, and whose sizeswere shown in FIG. 7.

DETAILED DESCRIPTION

As used in this specification, particles may be solid or liquid anddroplets are liquid.

As used in this specification “non-Newtonian” means a liquid which doesnot have a linear relationship between shear stress and fluid strainrate. Generally non-Newtonian liquids exhibit shear thinning(pseudoplastic) or shear thickening (dilatent). All gases, water (saltand fresh) and most unpolymerized hydrocarbons are Newtonian liquids.

As used herein “visco-elastic liquid” means a liquid which has conjointviscous and elastic properties. Typically these materials tend to bemore viscous than water and if deformed under shear will tend to returnto their pre-shear condition if the shear is removed.

The fluid to be atomized in accordance with the present invention andthe continuous phase fluid (suspending liquid or medium) are immiscible.

The immiscible fluids useful in accordance with the present invention toform a dispersed phase are non-Newtonian fluids, preferablynon-Newtonian liquids.

The non-Newtonian liquids used in accordance with the present inventionmay also be visco elastic liquids.

Typically the Non-Newtonian and visco-elastic liquids to be atomized toform the dispersed phase are partially polymerized monomers typicallypolymerized at least to 25%, generally from 25 to 50%, preferably from30 to 45%, most preferably from 30 to 40% conversion of monomers orsolutions of one or more polymers in one or more monomers listed below,having dissolved therein typically not less than 25 weight %, generallyfrom 25 to 50 weight %, preferably from 30 to 40 weight % of thepolymer. Typically the polymer will be a co- or homopolymer of themonomers listed below. However other polymers may be used, such aspolyolefins (e.g. polyethylene), polycarbonates (polyphenylene oxides)and impact (rubber modified) forms of such polymers such as high impactpolystyrene (HIPS). The impact modified polymers typically contain as adispersed phase from about 2 to 30, weight % of one or more rubbersselected from the group consisting of:

(a) co- or homopolymers of C₄₋₆ conjugated diolefins (i.e. dienerubbers);

(b) random, block, and tapered copolymers comprising from 30 to 70,preferably from 40 to 60, weight % of one or more C₈₋₁₂ vinyl aromaticmonomers which are unsubstituted or substituted by a C₁₋₄ alkyl radical;and from 70 to 30, preferably from 60 to 40 weight % of one or moreC.₄₋₆ conjugated diolefins (e.g. styrene butadiene rubbers or SBR); and

(c) copolymers comprising from 5 to 50 weight % of acrylonitrile ormethacrylonitrile and from 50 to 95 weight % of one or more C₄₋₆conjugated diolefins (e.g. nitrile rubbers).

The polymers may also include acrylonitrile butadiene styrene (ABS)polymers and butyl acrylate (homopolymer) modified poly acrylates suchas poly methyl methacrylate or styrene acrylates such as polymerscomprising from about 5 to 50 weight % of methyl methacrylate and fromabout 50 to 95 weight % of a vinyl aromatic monomer as described above.The polymer may be a polyolefin such as polyethylene or copolymers ofethylene and up to about 20 weight % of a C₄₋₈ mono, preferably alpha,olefin such as butene, hexene and octene or a copolymer of ethylene andup to about 40 weight % of an ethylenically unsaturated carboxylic acidsuch as a copolymer of ethylene and acrylic acid. Such solutions ofpolymers in monomers are also non-Newtonian visco elastic immiscibleliquids. The monomers or mixture of monomers suitable for use in thepresent invention to form a dispersed phase include any monomer ormonomers which can be emulsion or suspension polymerized. Typically theone or more monomers may be selected from the group consisting of C₈₋₁₂vinyl aromatic monomers which are unsubstituted or substituted by up totwo substituents selected from the group consisting of C_(1-4 alkyl)radicals; acrylonitrile; methacrylonitrile; maleic anhydride; malimide;and C₁₋₄ alkyl esters of C₁₋₆ monocarboxylic acids.

Suitable vinyl aromatic monomers include styrene, alpha methyl styreneand para methyl styrene. Suitable alkyl esters of C₁₋₆ monocarboxylicacids include methyl methacrylate, ethyl methacrylate, butylmethacrylate, methyl acrylate, ethyl acrylate and butyl acrylate.

Preferably the monomer is styrene which has been polymerized from 25 to50% conversion, typically from 30 to 45%, preferably from 30 to 40%conversion.

Generally the liquid to be atomized will have a viscosity between 0.1and 4000 centipoise (cP) preferably between 100 and 2500 cP, mostpreferably between 100 and 2000 cP.

The continuous phase (suspension medium) is preferably selected toenhance the production of the uniform droplets of the immiscible liquid.Preferably the viscosity of the continuous phase may be up to about 150cP. Droplet formation (atomization) and their subsequent movementthrough the suspension medium may be easier and more effective when theviscosity of the continuous phase is the same order of magnitude or lessthan the viscosity of the dispersed liquid. Generally, the suspensionmedium has a viscosity in the range from 0.01 to 400 cP. The viscosityof the continuous phase may be from about 0.01 to about 1, preferablyfrom about 0.05 to about 0.5 times the viscosity of the atomized liquid,and viscosity of the continuous phase may range from 0.1 to 400 cP,typically up to 150 cP, most preferably about 1 to 100 cP.

In addition, the suspension medium may have a sufficiently differentdensity from that of the atomized liquid. Preferably the density of thesuspending medium is greater than or equal to the density of thedroplets of the atomized liquid, with the density of the suspensionmedium typically being from about 1.02, to about 1.2, times the densityof the droplets of atomized liquid. If the atomized liquid (e.g. thedispersed phase) is further polymerized the density of the droplets orparticles of the dispersed phase may change and typically increase.Alternatively, if the droplets of the atomized liquid were to descendthrough the suspension medium, the density of the suspension medium maybe from about 0.98 to about 0.90 times the density of the droplets ofatomized liquid.

The continuous phase is suitably any inert liquid which is immisciblewith the partially polymerized monomer or polymer in monomer solution.The term “immiscible” meaning less than about 1 weight percent of thepartially polymerized monomer or polymer in monomer solution is miscible(or soluble) in the suspending liquid (i.e. the continuous phase doesnot solvate more than about 1 weight percent of the partiallypolymerized monomer or polymer in monomer solution). Preferably lessthan about 0.1 weight percent of the partially polymerized monomer orpolymer in monomer solution is miscible in the suspending liquid.

Typically, the continuous phase (suspending liquid) is water. However,mixtures of water with one or more water-miscible organic liquids suchas the lower alkyl alcohols such as methanol or butanol may be used. Theaddition of organic liquids which are immiscible with the dispersedphase and may or may not be immiscible with the continuous phase, andsalts may be used to vary (increase) the density of the continuousphase. Preferably, water is employed as the continuous phase.

Generally in the practice of this invention, the continuous phase(suspending liquid) will contain a surfactant or suspending aid. Howeverit is also possible to add the suspending aid to the liquid to beatomized. Suitable suspending aids are those materials which enable theformation of the monomer phase into spheroidal droplets of a desiredsize and which hinder the coalescence or secondary dispersion (breakage)of the thus-formed droplets.

Suspension stabilizers are well known in the art and comprise organicstabilizers, such as poly (vinyl alcohol), preferably hydrolyzed atleast 70%, typically up to 95%, preferably at no more than 98% andhaving a weight average molecular weight from about 30,000 to 300,000,typically from 75,000 to 300,000; carboxymethy cellulose typicallyhaving a weight average molecular weight up to 500,000; gelatine; agar;polyvinyl pyrrolidine; polyacrylamide; inorganic stabilizers, such asalumina, bentonite, magnesium silicate; surfactants, such as sodiumdodecyl benzene sulfonate; or phosphates, like tricalciumphosphate,disodium-hydrogen phosphate, optionally in combination with any of thestabilizing compounds mentioned earlier. In some cases the stabilizereffectiveness may be enhanced by using an extender. One skilled in theart may readily determine the usefulness of any particular stabilizer orcombination of stabilizers and/or extenders. The amount of stabilizermay suitably vary from 0 up to 10 weight %, usually 0.01 to 10,preferably 0.1 to 8, most preferably 0.1 to 5% by weight, based on theweight of the continuous phase and depending on the viscosity of liquidto be atomized (e.g. higher viscosity liquids require more stabilizer).If the suspending aid or stabilizer is added to the liquid to beatomized it may be added in an amount to provide the same amount ofstabilizer.

The suspension stabilizer should be capable of forming a surface betweenthe continuous phase and the dispersed liquid having an interfacialtension of not less than 3, preferably not less than 8, most preferablygreater than or equal to 12 dynes /cm.

In accordance with the present invention, one or more members selectedfrom the group consisting of initiators, anti-static agents oradditives, flame retardants, pigments (colorants) or dyes, fillers,stabilizers (UV and /or heat and light), coating agents, plasticizers,chain transfer agents, crosslinking agents, nucleating agents, andinsecticides and or rodenticides may be added to either the liquid to beatomized, the continuous phase, or both, in an amount from 0 up to 10weight %, typically from 0.1 to 10, and generally 0.05 to 8, butpreferably from 0.1 to 5 weight % of the liquid to be atomized.

Suitable initiators are organic peroxy compounds, such as peroxides,peroxy carbonates and peresters. Typical examples of these peroxycompounds are C₆₋₂₀ acyl peroxides, such as decanoyl peroxide, benzoylperoxide, octanoyl peroxide, stearyl peroxide, peresters, such ast-butyl perbenzoate, t-butyl peracetate, t-butyl perisobutyrate,t-butylperoxy 2-ethylhexyl carbonate, carbonoperoxoic acid,(1,1-dimethylpropyl) (2-ethylhexyl) ester, hydroperoxides anddihydrocarbyl peroxides, such as those containing C₃₋₁₀ hydrocarbylmoieties, including di-isopropyl benzene hydroperoxide, di-t-butylperoxide, dicumyl peroxide or combinations thereof.

Other initiators, different from peroxy compounds, are also possible, asfor example azides such as 2,2′-azobisisobutyronitrile. The amount ofinitiator is suitably from 0.01 to 1.00 weight %, based on the amount ofliquid to be atomized.

The continuous liquid or the liquid to be atomized may also contain ananti-static additive or agent; a flame retardant; a pigment (colorant)or dye; a filler material, plasticizers, such as white oil. Thecontinuous liquid or the liquid to be atomized may also contain coatingcompounds typically comprising silicones; metal or glycerolcarboxylates, suitable carboxylates include glycerol mono-, di- andtri-stearate, zinc stearate, calcium stearate, and magnesium stearate;and mixtures thereof. Examples of such compositions have been disclosedin GB Patent No. 1,409,285 and in Stickley U.S. Pat. No. 4,781,983. Thecoating composition can be applied to the particles via dry coating orvia a slurry or solution in a readily vaporizing liquid in various typesof batch and continuous mixing devices. This coating aids in preventingthe foamed cellular particles from forming agglomerates during thepre-expansion stage, and therefore, aids in improving the quality of themolded foamed article.

The continuous liquid phase or the liquid to be atomized, or both maycontain various additives such as chain transfer agents, suitableexamples including C₂₋₁₅ alkyl mercaptans, such as n-dodecyl mercaptan,t-dodecyl mercaptan, t-butyl mercaptan and n-butyl mercaptan, and otheragents such as pentaphenyl ethane and the dimer of α-methyl styrene. Theliquid to be atomized, or the continuous phase may contain cross-linkingagents, such as butadiene and divinylbenzene, and nucleating agents,such as polyolefin waxes. The polyolefin waxes, i.e., polyethylenewaxes, have a weight average molecular weight of 500 to 5,000. The waxesmay be used in a quantity of 0.05 to 1.0% by weight, based on the amount(weight) of the liquid to be atomized. The continuous phase or theliquid to be atomized may also contain from 0.1 to 0.5% by weight, talc,organic bromide-containing compounds, and polar agents as described ine.g. WO 98/01489 which may comprise alkylsulphosuccinates,sorbital-C₈-C₂₀ carboxylates, and C₈-C₂₀ alkylxylene sulphonates.Nucleating agents may be incorporated in the continuous phase or theliquid to be atomized, or both and they are particularly useful becausethey tend to improve the formation of cells if the invention is used toform foamable polymers.

Suitable insecticides are disclosed in U.S. Pat. Nos. 6,153,307 and6,080,796. These include boron compounds (borates and boric acid). Someuseful insecticides may be selected from the group consisting of1-[(6-chloro-3-pyridinyl)methyl]-4,5-dihydro-N-nirto-1H-imidazol-2-amineand 3-(2,2-dichloroethenyl)-2,2-di-methylcyclopropanecarboxylic acidcyano (3-phenoxyphenyl)-methyl ester (cypermethrin), the activeingredient in, for example, Demon TC sold by Zeneca;3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropanecarboxylic acid(3-phenoxyphenyl) methyl ester (permethrin), the active ingredient in,for example, Dragnet FT and Torpedo sold by Zeneca; and1-[(6-chloro-3-pyridinyl)methyl]-4,5-dihydro-N-nirto-1H-imidazol-2-amine(imidacloprid), the active ingredient in, for example, Premise sold byBayer.

In one embodiment the liquid to be atomized contains from 0 to about 40,preferably from 3 to 20, most preferably from 8 to 15 weight % of waterto produce polymer particles having from 4 to 16% of water as taught inU.S. Pat. No. 6,176,439. Or the liquid to be atomized may contain from 1to 20, most preferably from 3 to 15 weight % of water as taught incolumn 3, lines 19-26 of U.S. Pat. No. 6,160,027 (WO98/01489) discussedabove. The text of these patents is herein incorporated by reference.

The pressure atomizers used in accordance with the present inventiontypically are circular orifices and have diameters from 0.01 to 2,preferably from 0.1 to 1, most preferably from 0.1 to 0.8 mm, desirablefrom 0.1 to 0.5, most desirable from 0.1 to 0.4 mm and a length lessthan about 5 mm. Generally, the atomizer will have a length to diameter(L/D) ratio ranging from about 0.2 to about 10, preferably from 0.2 to5.

For industrial-application the liquid to be atomized may be injectedinto the continuous phase using an atomizer or a header plate containingatomizers (e.g., a plate having a number of holes of the abovedimensions therein). The number of atomizers which may be accommodatedin a header plate will depend on the size of the plate and the size andspacing of the atomizers. A header plate may contain multiple atomizersprovided their operations do not interfere with each other. Care shouldbe taken to minimize the interaction between atomized streams,particularly in the vicinity of the atomizer exits. There is a need tospace the individual atomizers sufficiently far apart to minimize theinteraction between adjacent streams from adjacent atomizers. Excessiveinteractions between adjacent streams may cause deformation of theatomized droplets due to their direct collisions or may lead topremature dispersion of the streams (e.g. the continuous stream ofliquid to be atomized) into droplets. The interactions between adjacentstreams of liquid to be atomized do not appear to be significant whenadjacent streams are separated by a distance of at least 5, preferably10 times the average diameter of the atomized droplets.

The atomizers may be equally spaced in a square or other pattern overthe entire surface of the header plate.

In order to reduce viscosity of the liquid to be atomized to improvequality of atomization, in one embodiment of the invention heat isapplied to the liquid to be atomized at one or more locations selectedfrom the group consisting of the storage tank for the liquid to beatomized, the transfer line from the storage tank to the atomizer inlet,and the atomizer.

The liquid to be atomized contained in the storage tank and/or in thetransfer line may be heated to a temperature from ambient (20° C.) up tobelow the decomposition point of the components of the liquid (e.g.decomposition point of polymer in the liquid to be atomized). In oneembodiment of the invention the temperature may be the set temperatureof the process if, for example, the atomized liquid is to be polymerizedup to about 135° C. The temperature may range from at least about 30°C., preferably not less than 45° C., and most desirably not less than50° C. Generally temperatures from about 50° C. to 95° C. are useful(for atomization).

The atomizers may also be heated to similar temperatures. For example,the exit part of the atomizer comprising the orifice plate could beheated with a circulating liquid such as water or another heattransferring liquid or, preferably could be heated by other means suchas electrical heaters.

The liquid to be atomized may be dispersed in the continuous phase in anamount from about 0.01 to 60 volume %, preferably from about 10 to 50volume %, and most preferably from about 15 to 45 volume %. Additives,as discussed above, may be added to the continuous phase in a totalcombined amount from 0.01 to 15, volume %, and preferably 0.05 to 10volume %.

The liquid to be atomized is added to the continuous phase at a ratefrom 0.05 to 15, typically 0.1 to 12, and preferably 0.5 to 10ml/sec/per atomizer. The liquid is passed through the atomizer locatedbelow free surface of the continuous phase and forms a liquid streamwithin the continuous phase and this stream disperse downstream theatomizer exit as the liquid droplets in the continuous liquid phase. Theaverage size of the atomized droplets is determined by the atomizergeometry, monomer exit velocity from the atomizer and properties of bothcontinuous and atomized phases. A higher viscosity suspending medium maybe employed in the preparation of larger droplets of atomized liquid.Typically the droplets will have an average size from about 0.1 to 10mm, typically from 0.1 to 5 mm, preferably from 0.3 to 3 mm. Forrelatively uniform atomized droplets the standard deviation for sizedistribution is typically less than about 10% (preferably less than 8%)of the average droplet diameter of atomized liquid. Typically for adroplet size from about 0.3 to 5 mm the standard deviation from the meandroplet droplet is from about 0.03 to 0.35 mm (e.g. not more than 8% ofthe average droplet diameter). It should be noted that the averagedroplet diameter is substantially larger than the diameter of theatomizer.

The liquid to be atomized is forced through the atomizer(s) underpressure. Typically the pressure is not greater than 100 bars (e.g. 3 to100 bars), typically from 3 to 80, preferably from 5 to 60 bars. Thepressure energy of the atomized liquid is converted in an atomizer to astream kinetic energy. This kinetic energy further leads to streamdisintegration when a stream interacts with the atomizer orifice exitand with the surrounding continuous phase. This interaction generates adisturbance which breaks the stream into droplets either at the atomizerexit or the disturbance propagates downstream within the stream andbreaks the stream into droplets at some distance further from theatomizer exit. In one embodiment of the invention the pressure of theflowing liquid to be atomized is subject to continuous or intermittentpulsation upstream of the atomizer inlet of less than 20%, typicallyfrom 1 to 10, preferably from 3 to 10%, of the static pressure of theatomized liquid. The frequency of the pulsation depends, among otherparameters, on the viscosity of the atomized liquid and may range from 1to 500, preferably less.than 200 Hz, generally less than 150 Hz. Theimposed pressure pulsation strengthens and amplifies the originaldisturbance generated by the stream-atomizer interaction in a way thataffects droplet size distribution and, usually, makes it more uniform.By adjusting frequency and amplitude of the imposed pressure pulsation,a dual size or customized distributions can be generated. In the case ofatomization of more viscous Non-Newtonian liquids, pressure pulsationcan be imposed as a primary mechanism/source of stream breakup (dropletformation).

Preferably, the atomization may take place directly into a reactor underthe free surface of the continuous phase or it may take place into aholding tank for subsequent transfer to a reactor. The atomized dropletsshould be maintained under shear and turbulence conditions whichminimize droplet interaction and provide a low momentum movement of thedroplets in order to decrease probability of droplet agglomeration orsecondary breakup. Generally, the conditions should require a flowpattern within the continuous phase with low, preferably relativelyuniform, shear and low and controlled turbulence level. Advantageously,the continuous phase may be subjected to laminar motion, whichpreferably, should be substantially uniform through the continuous phasevolume, as opposed to a local laminar motion zone which a low speedimpeller may generate.

Such conditions are particularly important if the atomized droplets aresubsequently processed or polymerized and the initial size distributionshould be either maintained during the process, or improved, or modified(reduced) in a controlled manner, resulting in the required final sizedistribution of the bead product.

During the processing or polymerization, the liquid droplets or solidparticles of the dispersed phase should usually remain submerged belowthe free surface of the continuous phase and be thoroughly (uniformly)distributed in the continuous phase in a way that minimize theirinteraction, (e.g. particle or droplet collision) but also providesother requirements, for :example an adequate heat transfer.

The proposed method for maintaining such conditions is a process forcreating a low shear flow pattern with a controlled low turbulencelevel, without mechanical agitation, in a continuous liquid phasecontained a vessel, comprising continuously or periodically injectinginto selected part(s) of the vessel a stream of fluid immiscible andinert to the vessel contents and having a density lower than the reactorcontents, and retrieving this fluid above free surface of liquid phaseand, preferably, reinjecting it back to the vessel. Preferably, theinjected fluid is an inert gas not soluble in the continuous anddispersed phases.

If the initial particle size distribution needs to be preserved to thelargest extent during processing, the dispersed particles, ideally,should be distributed uniformly within a volume of the continuous phase,exposed to a low shear and remain in a laminar motion within thecontinuous phase.

There is also an option that the initial particle size distribution maybe improved to become more uniform and the average diameter slightlyreduced. In this option, a certain percentage of the largest particles(e.g. up to 15% of the largest particles) in the population should bebroken in a controlled manner, by being exposed to low turbulence lowshear flow pattern in the continuous phase.

In a further embodiment the entire particle size distribution can bereduced by causing a secondary break up of majority (e.g. at least 85%)of the droplets in the dispersed phase.

In accordance with the present invention, the required flow pattern canbe created in the vessel by injecting one or more streams of a fluidhaving a density substantially lower than the continuous and dispersedphases and inert and immiscible with the reactor contents, into selectedlocations, preferably including the bottom parts of the reactor orvessel volume. The fluid may be continuously or periodically injected,(to keep the dispersed phase from sinking to the bottom of the reactoror rising to the free surface of the continuous phase), with acontrolled frequency of injection depending on the ratios of densitiesand volumes of the continuous and dispersed phases.

Preferably, such a fluid with a sufficiently low density suitable forinjection is a gas. The gas may be selected from the group consisting ofinert gases, not soluble in continuous phase, air and nitrogen,preferably nitrogen. The gas may be injected into the continuous phaseat gauge pressure up to 15 bar (e.g. from 0.001 to 15 bar gauge). Thegauge pressure referred to in this specification is the differencebetween the absolute static gas pressure upstream the gas injectionport, and the combined (sum of) hydrostatic pressure of continuousliquid in a vessel and an absolute ambient static pressure above freesurface of continuous phase.

If gas is selected as the fluid injected to the reactor, two modes ofinjection are possible.

The first and preferred mode of injection is to inject gas at lowpressure (preferably less than 3 bar gauge) through the injection ports,so the injected gas forms streams of bubbles in the continuous phasedownstream the injection ports, with the average size of a bubblesubstantially larger (e.g. at least two times, preferably five times)than the average diameter of the dispersed phase droplets. Due to thebalance of buoyancy, gravity add drag forces, the bubble stream risestowards the free surface of the continuous phase where the gas isrecovered and, preferably, recycled back to the vessel. As the gasbubble stream flows towards the free surface, it interacts with thecontinuous liquid phase and its momentum creates a flow pattern in thereactor, forcing the continuous phase into a circular low shear, lowturbulence motion creating a recirculation zone in the reactor. Thevelocity gradients and geometry of the generated zone can be controlledby the geometry (number, diameters and locations) of the gas injectionports and by gas flow rate. The dispersed particles or droplets flowwithin the recirculation zone and are subjected to the sufficiently lowshear rate and turbulence so that they remain submerged withoutexcessive mutual interaction, their momentum sufficiently low, so evenwhen they collide—the probability of agglomeration or breakup resultingfrom such a low impact collision remaining very low. This motion ofparticles can be maintained for particles which are lighter than thecontinuous phase and for the particles which are heavier than thecontinuous phase, providing that the density difference betweendispersed and continuous phase is typically within the range of ±20%(i.e. the ratio of the density of the dispersed phase to the density ofthe continuous phase may range from 0.8:1 to 1.2:1).

Preferably, the injection ports have diameters substantially (e.g. atleast two times) larger than the average diameter of the disperseddroplets. The locations of the gas injection ports are selected based onthe concentration of the dispersed phase and the dispersed particledensity. Generally, the injection ports should be located in the reactorbelow the layer of the dispersed phase contained in the continuousphase. Accordingly, to submerge dispersed particles having a densitylower than the density of the continuous phase and to prevent theirfloating motion, the injection ports should be beneath the floatingparticle/droplet layer and can be located in the reactor walls or in thebottom.

To elevate particles/droplets heavier than continuous phase and toprevent their sedimentation on the vessel bottom, some of the injectionports have to be located in the bottom of the reactor. In this case, amodification of the geometry of the reactor bottom, e.g. into aninverted conical or frustroconical type of a shape, may be desirable. Inone embodiment of the present invention (FIG. 1) the reactor bottom isinverted conical, with one injection port situated in the tip of thecone and two other ports located tangentially to the cone cross section,at the level of half-height of the cone.

If the density of the dispersed particles changes during the process, asfor example during polymerization of the dispersed monomer droplets, acombination of both types of port arrangements (i.e. in the reactorwalls and bottom) can be used. The most useful general arrangement ofthe port locations is with the main ports located in the reactor bottomand, optionally, some supporting ports in the lower parts (e.g. bottomhalf, preferably bottom quarter) of the reactor walls.

Mainly, the gas injection rate determines the level of turbulence in thecreated flow pattern in the reactor. The gas injection rate will dependon a number of factors including the volume and density ratios of thedispersed and continuous phases; the viscosity of the continuous phase;the geometry of the vessel; and the size of the particles of thedispersed phase. Suitable gas injection rates may be determined by oneskilled in the art by repeating experiments similar to those containedherein.

Generally, to preserve the initial size distribution of the dispersedparticles or droplets to the largest extent, the level of turbulence ofthe continuous flow phase in the reactor has to be sufficiently low sothe motion of the reactor contents is laminar.

If required, the initial particle or droplet size distribution can bealso modified to a certain extent during the processing by properlyadjusting, gas flow rate. Although the average particle size cannot beincreased by a controlled agglomeration of particles, it can be reducedin some cases or improved towards more uniform distribution byincreasing the gas injection rate to cause the breakup of only thelargest particles (e.g. the 15% of the largest particles) in thepopulation. The breakup is caused by the controlled increase of theturbulence level within the flow pattern created by the gas bubbles, andnot by particle or droplet interaction (e.g. collision).

In the further embodiment of the present invention, the average particlesize of the dispersed phase can be substantially reduced by causing abreak up of majority (e.g. at least 85%) of the droplets in thedispersed phase. In this embodiment a flow pattern with higher shear andturbulence level is generated in the continuous phase by applying highergas injection rates, to break up the droplets.

The second mode of gas injection can be applied only in the processeswhere the dispersed particles which are to be distributed and suspendedhave a density lower than the continuous phase. In this mode gas isinjected at high pressure, typically 5 bar (gauge) and above, togenerate a large number of very small gas bubbles, distributed withinthe volume of the continuous phase. The injection ports have diametersat least an order of magnitude, preferably, several orders of magnitudessmaller than the average diameter of the dispersed particles. Theconcentration of gas bubbles should be sufficiently high so theeffective density of the continuous phase becomes reduced to a valuelower than the density of the dispersed phase and, as the result, thedispersed particles start to sink. In this mode the periodic gasinjection can be particularly useful in creating an “oscillatory”movement of the particles or droplets, as during the injection periodthe particles or droplets sink and next when gas supply is shut off andgas bubbles leave the continuous phase exiting through the free surfaceof the continuous phase, the particles rise from the bottom part of thevessel or reactor and float again towards the free surface. The next gasinjection should take place before the particles of the dispersed phasereach the free surface of the continuous phase. The mechanismresponsible for small size of bubbles is mainly turbulence of a gasstream. Bubbles rise towards the free surface, usually with highvelocity, their residence time in a continuous phase is brief but theflow pattern generated in the continuous phase can be at a much higherturbulence level than in the first mode of injection. Therefore wherenecessary, care should be taken not to break floating particles ordroplets. In this mode of injection, a higher viscosity (typically 10 cPor higher) of the continuous phase is advantageous, as it slows down thegas bubbles increasing their residence time in the continuous phase andreduces the overall level of turbulence in the vessel.

Typically, the polymerization of the dispersed droplets will be to notless than 90%, preferably 95%, most preferably 99.5% or to a greaterconversion. The continuous liquid will be heated during the process, asdiscussed above, to temperatures up to 135° C., typically not more than130° C.

The resulting particles may be used in a number of applications such asion exchange resins or applications requiring a uniform or customizedparticle size distribution.

However, in a further embodiment of the invention, the polymerization ofthe atomized liquid takes place in the presence of a blowing agent. Theblowing agent may be incorporated in the continuous liquid phase or theliquid to be atomized. If the blowing agent is in the continuous liquidphase it may be present in amounts from 2.5 to 7 weight % based on theweight of the atomized liquid. If it is introduced into the liquid to beatomized it would be used in corresponding amounts.

In another embodiment the polymerization may be finished and theresulting polymer beads are obtained and subsequently impregnated with ablowing agent. The polymer beads or particles would be re-suspended in aliquid medium, such as water and the medium would additionally containfrom 2.5 to 7 weight % based on the polymerized dispersed liquid (e.g.polymer beads) of a blowing agent.

Suitable organic blowing agents are well known to those skilled in theart and are typically selected from the group consisting of: acetone,methyl acetate, butane, n-pentane, hexane, isobutane, isopentane,neopentane, cyclopentane and cyclohexane and mixtures thereof. Otherblowing agents used in making polymer particles expandable are HFC'S,CFC'S, and HCFC'S, and mixtures thereof. In some cases water may be usedas a blowing agent for example as disclosed in EPO applications99947397.8, 99952459.8 and 97932783.0.

Preferably, in the present invention, the blowing agent is selected fromthe group consisting of acetone, methyl acetate, butane, n-pentane,cyclopentane, isopentane, isobutane, neopentane, and mixtures thereof. Apreferred blowing agent is normal pentane and mixtures of pentane. Theforegoing blowing agents may also be used in combination with carbondioxide, air, and nitrogen.

The present invention will now be illustrated by the followingnon-limiting examples, all of them comprising polymerization of theatomized partially polymerized styrene droplets, suspended in the flowpattern created by gas injection into continuous phase according to thefirst preferred mode.

Experimental Set Up.

The pressure atomization experimental set up is schematically shown inFIG. 1. The liquid to be atomized was placed in a cell or chamber 1. Atthe top of the cell a plunger 2 was inserted to apply static pressure tothe liquid and to control the flow rate of liquid to be atomized throughthe atomizer 15. The plunger 2 was driven by a screw actuator 3 and aservo motor 4. The outlet 5 from the cell 1 was connected to a transferline 6. Portions or the entire length of the transfer line 6 werejacketed 7 to apply heat to the flowing liquid. The static pressure ofthe liquid in the transfer line 6 was measured by a static pressuretransducer 8. A pressure pulsation generator 9 was also connected to thetransfer line 6 in a way that it generated pressure pulsation by amechanical motion in the direction perpendicular to the flow of theto-be-atomized liquid. The resulting instantaneous pressure of theliquid to be atomized was measured by the fast response pressuretransducer 11 also connected to the transfer line 6. A thermocouple 10was in the transfer line to control the heat applied to the liquidflowing in the line. The transfer line 6 delivered the liquid to beatomized to an atomizer 15, located in the bottom of a reactor 14,filled with a continuous liquid phase (water with stabilizing agent) 13.The reactor was jacketed 12 so it could be heated or cooled. Theatomizer could be changed to provide a different diameter and L/D ratio.

A sample of the continuous phase containing about several thousand ofatomized liquid droplets was analyzed for the particle size distributionby viewing it via camera under a 7× microscope and taking photographs ofthe droplets. Then the photographs were processed by a computer todetermine the droplet diameters, (using commercially availablesoftware). The size distribution, including the average diameter and thestandard deviation were calculated and the results were converted (usingcustomized software) to generate the plots shown in the Figures.

The experimental set up to maintain the pressure atomized particles inlow shear controlled turbulence flow pattern, which is a more detailedsketch of the reactor 14 in FIG. 1, is shown in FIGS. 2 and 3.

In FIGS. 2 and 3, the reactor vessel 14 having a heat jacket 12 waspartially filled with a continuous water phase 13 mixed with thestabilizing agent and a dispersed phase 16 of partially polymerizedstyrene monomer. At the bottom of the reactor was a vertical gasinjection port 17 and on the sides of the bottom half of the reactorwere two tangential injection gas ports 18. An exit line 19 draws gasfrom above the free surface of the continuous phase 13 and gas can beremoved from the top of the reactor 20 either to the exhaust stack orrecirculated, using a blower, back to injection ports 17 and 18 toinject gas back into the continuous phase in the vessel. Nitrogen wasselected as the injection gas and was introduced into the injectionports at gauge pressure of less than 0.05 bar generating strings orstreams of large bubbles 21, with approximate diameter of 15-20 mm.

At the end of each experiment the equipment was drained and cleaned forthe next experiment.

Atomization

In all atomizations, pressure pulsation was applied to modulate the flowof liquid to be atomized.

A solution of styrene monomer prepolymerized to 35 wt % mixed withbenzoyl peroxide (BPO) or dilauryol peroxide initiators, eitherpre-heated to ˜45° C. in the transfer line or at ambient temperature,were dispersed by pressure atomization into the jacketed reactorcontaining the continuous phase comprising water and 3 wt % polyvinylalcohol as a stabilizer, the continuous phase being at ambienttemperature.

The flow rates of the atomized monomers ranged from 1.3 to 0.35 ml/sthrough the atomizer. The atomizer diameter was 0.3 mm. A pressurepulsation with the amplitude of about 8%-10% of the static pressure ofthe liquid to be atomized and at a frequency of up to 100 Hz was imposedon the pre-polymerized monomer flowing in the transfer line by thepulsation generator upstream the atomizer inlet.

Particle Size

A random sample of the continuous phase containing about several hundredof atomized liquid droplets was analyzed for the particle sizedistribution by viewing it via camera under a 7× microscope and takingphotographs of the droplets. Then the photographs were processed by acomputer to determine the droplet diameters, (using commerciallyavailable software). The cumulative size distribution including theaverage droplet diameter and the standard deviation of the sizedistribution were calculated (using commercially available software),and the results were converted (using customized software) to generatethe plots shown in the Figures. The similar procedure was used todetermine the size distributions of the polymerized beads.

EXAMPLES Example 1

The initial sizes of the monomer droplets had a relatively widedistribution and they were measured by collecting a random sample andanalyzing it via camera under a microscope. Initially, the dispersedphase had a density lower than continuous phase and the droplets wouldhave formed a layer floating at the free surface of the continuous phasein the reactor. To distribute the droplets within the reactor volume,nitrogen was injected through the central and two tangential injectionports in the bottom part of the reactor and the resulting stream ofbubbles created a flow pattern where the dispersed droplets weresuspended. To start the polymerization process the reactor contents wereheated to 90° C. and the temperature was maintained for the subsequent˜5 hrs. As polymerization progressed, the dispersed droplets started tosink as their density changed from <0.9 g/cm3 to ˜1.1 g/cm3. A randomsample of the fully polymerized bead product was analyzed for its sizedistribution and compared with the initial size distribution of thedroplets, as shown in FIG. 4. The size of beads is smaller than thedroplets due to density changes, but the overall shape of the initialdroplet size distribution has been retained in the size distribution ofthe product (i.e. beads).

Example 2

The initial size distribution of the monomer droplets was measured bycollecting a sample and analyzing it via camera under a microscope (7×magnification). To distribute the droplets within the reactor volume,nitrogen was injected through two tangential injection ports locatedabove the bottom of the reactor and through one port centrally locatedin the reactor bottom. The polymerization process was completed afterapproximately 5 hrs, keeping the reactor contents at a temperature of˜90° C. The resulting polymerized beads were analyzed for sizedistribution and compared with the initial size distribution of thedroplets as shown in FIG. 5. The cumulative weight percentage oversizecalculated for the initial droplets and for the final bead product isshown in FIG. 6, and the results indicate that smaller droplets retainedtheir size well during the polymerization process (considering change ofdensity) while large droplets were more prone to some secondarybreakups. However, the secondary breakups of the largest dropletsslightly improved the overall size distribution of the product making itmore uniform than the initial size of the droplets.

Example 3

The dispersed phase were the droplets of styrene monomer partiallypolymerized to 35%, pressure atomized at ambient temperature, withmodulation frequency 80 Hz and amplitude less than 8% of static pressureof the monomer. The initial size distribution of the droplets wasmeasured by collecting a random sample and analyzing it via camera undera microscope (7× magnification). To distribute the droplets within thereactor volume during polymerization process, nitrogen was injectedthrough two tangential injection ports located above the bottom of thereactor and through the port centrally located in the reactor bottom.The polymerization process was completed after approximately 5 hrs,keeping the reactor contents at a temperature of ˜92° C. The resultingpolymerized beads were analyzed for size distribution and compared withthe initial size distribution of the droplets, as shown in FIG. 7. Theresults of the comparison indicate that smaller droplets retained theirsize better during the polymerization process (considering change ofdensity) while large droplets were more receptive to some secondarybreakups. However, the overall cumulative size distribution of the beadproduct was improved and was more uniform as compared to the initialsize distribution of the droplets. The comparison results are shown inFIG. 8.

What is claimed is:
 1. A process comprising pressure atomizing from 0.01to 60 volume % of a non-Newtonian immiscible liquid having a density±20% of the density of a continuous liquid phase, at a pressure of atleast 5 bar, below the free surface of the continuous liquid phase whichmay be stationary or flowing, contained in a holding tank or a tank,pipe or loop reactor, to produce a dispersion of atomized droplets ofthe immiscible liquid having at least one controlled average diameterfrom 0.1 mm to 10 mm and processing/polymerizing the dispersed phase ina low shear flow pattern with a controlled low turbulence level created,without mechanical agitation, by continuously or periodically injectingat gauge pressure up to 15 bar into selected parts of the reactor one ormore streams of gas inert to the reactor contents having a density lowerthan the continuous phase and immiscible with the reactor contents andrecovering this gas from the top of reactor, above free surface of thecontinuous phase.
 2. A process according to claim 1, comprising passingthe liquid to be atomized through at least one atomizer having anopening diameter from 0.01 mm to 2 mm and an L/D ratio from 0.2 to 10,at a flow rate from 0.05 to 15 ml/second/per atomizer and at gaugepressure from 3 to 100 bar.
 3. The process according to claim 2, whereinthe continuous phase is a liquid having a viscosity up to 150 cP.
 4. Theprocess according to claim 3, wherein the continuous phase furthercomprises from 0.1 to 10 weight % based on the weight of the continuousphase of one or more suspension stabilizers.
 5. The process according toclaim 4, wherein the gas is selected from the group consisting of airand nitrogen.
 6. The process according to claim 5, wherein the said gasis injected at a gauge pressures up to 15 bar into the reactor throughinjection ports located in the bottom portion of the reactor and in thereactor walls.
 7. The process according to claim 6, wherein the liquidto be atomized further comprises from 0 to 10 weight % based on theweight of the liquid to be atomized of one or more members selected fromthe group consisting of initiators, anti-static agents, flameretardants, pigments, dyes, fillers, UV stabilizers, heat and lightstabilizers, coating agents plasticizers, chain transfer agents,crosslinking agents, nucleating agents, insecticides and rodenticides.8. The process according to claim 7, wherein the suspension stabilizeris polyvinyl alcohol having a molecular weight greater than 30,000,which has been hydrolyzed up to 98%.
 9. A process according to claim 8,wherein the flow of the liquid to be atomized may optionally bemodulated with a step-type amplitude at the constant frequency byimposing up stream of the atomizer a pressure pulsation of an amplitudeof less than 20% of the static pressure on the liquid and at a frequencyup to 200 Hz.
 10. The process according to claim 9, wherein the liquidto be atomized is selected from the group consisting of one or moremonomers which have been polymerized to from 25 to 50% and one or moremonomers having dissolved there in from 25 to 50 weight % of a polymersoluble is such monomers.
 11. The process according to claim 10, whereinthe one or more monomers are selected from the group consisting of C₈₋₁₂vinyl aromatic monomers which are unsubstituted or substituted by up totwo substituents selected from the group consisting of C_(1-4 alkyl)radicals, acrylonitrile, methacrylonitrile, maleic anhydride, malimide,and C₁₋₄ alkyl esters of C₁₋₆ monocarboxylic acids.
 12. The processaccording to claim 11, wherein the liquid to be atomized has a viscosityfrom 1 cP to 4000 cP.
 13. The process according to claim 12, wherein tothe liquid to be atomized is maintained a temperature from 20° C. to 95°C.
 14. The process according to claim 13, wherein the continuous phaseis water.
 15. The process according to claim 14, wherein the polyvinylalcohol is present in the continuous phase in an amount from 0.1 to 8weight % based on the weight of the liquid to be atomized.
 16. Theprocess according to claim 15, wherein said one or more monomers areselected from the group consisting of styrene, alpha methylstyrene, paramethylstyrene, methyl methacrylate, ethyl methacrylate, butylmethacrylate, methyl acrylate, ethyl acrylate and butyl acrylate. 17.The process according to claim 16, wherein the atomized liquid has aparticle size from 0.3 to 5 mm and a standard deviation from the meanparticle diameter is from 0.03 to 0.35 mm.
 18. The process according toclaim 17, wherein the atomizer has an orifice size from 0.1-0.8 mm, theflow rate through the atomizer is from 0.1 to 12 ml/s, and the staticpressure of the immiscible liquid is from 3 to 80 bars.
 19. The processaccording to claim 18, wherein the gas is injected into the continuousphase at a gauge pressure less than 3 bar and forms streams of bubbleshaving diameters substantially larger than the average size of thedispersed phase particles or droplets.
 20. The process according toclaim 18, wherein the dispersed phase has a density lower than thecontinuous phase and the said gas being injected periodically atpressures above 5 bar into the continuous phase to generate bubbles atleast an order of magnitude smaller than the average size of dispersedparticles or droplets, reducing the effective bulk density of thecontinuous phase.
 21. The process according to claim 19, wherein theinitial droplet size distribution is substantially preserved in thefinal polymer bead size distribution.
 22. The process according to claim19, wherein the initial droplet size distribution is modified so that upto 15% of the largest droplets are broken to provide a more uniformpolymer bead size distribution.
 23. The process according to claim 19,wherein the initial droplet size distribution is reduced so that themajority of the droplets population is broken into a smaller size. 24.The process according to claim 21, further comprising subjecting theatomized liquid to polymerization to not less than 75% conversion at atemperature up to 130° C.
 25. The process according to claim 22, furthercomprising subjecting the atomized liquid to polymerization to not lessthan 75% conversion at a temperature up to 130° C.
 26. The processaccording to claim 23, further comprising subjecting the atomized liquidto polymerization to not less than 75% conversion at a temperature up to130° C.
 27. The process according to claim 24, wherein saidpolymerization is conducted in the presence of from 2.5 to 7 weight %based on the weight of the atomized liquid of a blowing agent.
 28. Theprocess according to claim 24, wherein the polymerized particles ofatomized liquid are impregnated with from 2.5 to 7 weight % of a blowingagent after polymerization.
 29. The process according to claim 24,wherein the liquid to be atomized contains from 0 to 40 weight % ofwater.
 30. The process according to claim 25, wherein saidpolymerization is conducted in the presence of from 2.5 to 7 weight %based on the weight of the atomized liquid of a blowing agent.
 31. Theprocess according to claim 25, wherein the polymerized particles ofatomized liquid are impregnated with from 2.5 to 7 weight % of a blowingagent after polymerization.
 32. The process according to claim 25,wherein the liquid to be atomized contains from 0 to 40 weight % ofwater.
 33. The process according to claim 26, wherein saidpolymerization is conducted in the presence of from 2.5 to 7 weight %based on the weight of the atomized liquid of a blowing agent.
 34. Theprocess according to claim 26, wherein the polymerized particles ofatomized liquid are impregnated with from 2.5 to 7 weight % of a blowingagent after polymerization.
 35. The process according to claim 26,wherein the liquid to be atomized contains from 0 to 40 weight % ofwater.
 36. The process according to claim 20, further comprisingsubjecting the atomized liquid to polymerization to not less than 75%conversion at a temperature up to 130° C.
 37. The process according toclaim 36, wherein the initial droplet size distribution is substantiallypreserved in the final polymer bead size distribution.
 38. The processaccording to claim 37, wherein said polymerization is conducted in thepresence of from 2.5 to 7 weight % based on the weight of the atomizedliquid of a blowing agent.
 39. The process according to claim 37,wherein the polymerized particles of atomized liquid are impregnatedwith from 2.5 to 7 weight % of a blowing agent after polymerization. 40.The process according to claim 37, wherein the liquid to be atomizedcontains from 0 to 40 weight % of water.